If you are considering using GNS3 for your CCNA or CCNP labs but are reluctant to do so as you have heard that it requires an official Cisco IOS copy this article is worth reading. First GNS3 will require an Official Cisco IOS but there are a number of ways that you can obtain a copy. You can of course purchase a copy from Cisco or you can purchase a used router such as a 2610 and copy the IOS from it and finally if you are a Internet savvy person you can find one online and download it free.
Before you start out buying anything or surfing the web you need to know what to look for. Cisco has made changes to their CCNA and CCNP exams, these exams are now using Cisco’s IOS revision 15.0 or greater. Therefore you should strive to obtain this revision for your lab. Now for the bad news The Cisco 7200 is the only router within GNS3 that support the latest Cisco IOS release. The other routers will support 12.4 or earlier releases and if you plan on using them the 12.4 release is what you should look for as it supports a few command needed for CCNP studies that were not available in earlier releases.
All this being said I have done some searching of the internet and found the following site that may have more detailed information on the IOS releases available for router used in GNS3:
C1700 All Released Versions
C2600 All Released Versions
C2691 All Released Versions
C3620 All Released Versions
C3640 All Released Versions
C3660 All Released Versions
C3725 All Released Versions
C3745 All Released Versions
C7200 All Released Versions
Additionally here are a couple of tips when installing a Cisco IOS into GNS3. First make sure you are using a uncompressed copy of the IOS, this will reduce the time it takes for GNS3 to boot the routing device. The Cisco IOS release is a .bin file example “c2600-adventerprisek9-mz.124-19.bin” and is compressed. In most cases if you select this file when setting up your IOS in GNS3 you will be prompted if you wish to decompress the file in this case answer yes, but is come cases you will to do this manually in the instances you can use WIN7 to unzip the file, as a .image file. Second make sure to check the Cisco site the find out the minimum memory requirement as GNS3 is seldom correct in the value it allocates. This will cause the router to not boot properly or not at all. Lastly be sure to obtain an optimal IDEL-PC value as this will reduce the processor utilization by the routing devices in you labs.
There are many other tricks to using and optimizing GNS3 which I will cover in upcoming articles but if you chose to use GNS3 I know you will find it to be an excellent alternative to purchasing real hardware.
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